<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>nest</title>
  </head>
  <body>
    <canvas id="theCanvas"></canvas>
    <script>
      const theCanvas = document.getElementById("theCanvas"),
        ctx = theCanvas.getContext("2d"),
        current_point = {
          x: null, //当前鼠标x
          y: null, //当前鼠标y
          max: 20000,
        };

      let canvas_width = (theCanvas.width = window.innerWidth || document.documentElement.clientWidth || document.body.clientWidth),
        canvas_height = (theCanvas.height = window.innerHeight || document.documentElement.clientHeight || document.body.clientHeight),
        random_points = [],
        all_points = [];

      theCanvas.style = "position: fixed; top: 0px; left: 0px;";

      function draw() {
        //清屏
        ctx.clearRect(0, 0, canvas_width, canvas_height);
        let i, pi, x_dist, y_dist, dist, w;

        //遍历点集合绘制线条，类似于握手问题，两个点只绘制一条线
        random_points.forEach((p, index) => {
          (p.x += p.xa), //按指定速度移动
            (p.y += p.ya),
            //小球碰撞则速度取相反数
            (p.xa *= p.x > canvas_width || p.x < 0 ? -1 : 1),
            (p.ya *= p.y > canvas_height || p.y < 0 ? -1 : 1),
            ctx.fillRect(p.x - 0.5, p.y - 0.5, 1, 1); //绘制点

          for (i = index + 1; i < all_points.length; i++) {
            pi = all_points[i];
            if (pi.x !== null && pi.y !== null) {
              x_dist = p.x - pi.x;
              y_dist = p.y - pi.y;
              dist = x_dist * x_dist + y_dist * y_dist;
              //当两点距离小于极限距离时会产生连线，当第二个点是鼠标所产生点时，第一个点在范围内会产生向鼠标点的速度，产生吸附效果
              dist < pi.max && pi === current_point && dist >= pi.max / 2 && ((p.x -= 0.03 * x_dist), (p.y -= 0.03 * y_dist));
              //根据距离计算连线的透明度，使过度效果流畅
              w = (pi.max - dist) / pi.max;
              ctx.beginPath();
              ctx.lineWidth = w / 2;
              ctx.strokeStyle = `rgba(110,110,110,${w + 0.2})`;
              ctx.moveTo(p.x, p.y);
              ctx.lineTo(pi.x, pi.y);
              ctx.stroke();
            }
          }
        }),
          requestAnimationFrame(draw);
      }

      //绑定事件，判断是否添加鼠标这个点
      window.onmousemove = (e) => {
        e = e || window.event;
        current_point.x = e.clientX;
        current_point.y = e.clientY;
      };
      window.onmouseout = () => {
        current_point.x = null;
        current_point.y = null;
      };

      //随机生成100个点
      for (let i = 0; i < 100; i++) {
        let x = Math.random() * canvas_width, //初始坐标
          y = Math.random() * canvas_height,
          xa = 2 * Math.random() - 1, //x速度
          ya = 2 * Math.random() - 1, //y速度
          max = 6000; //会产生连线的距离的平方

        random_points[i] = { x, y, xa, ya, max };
      }
      //将鼠标的点添加至点集合中
      all_points = [...random_points, current_point];

      //只是背景特效-所以延迟执行
      setTimeout(draw, 100);
    </script>
  </body>
</html>
